This invention relates to printing presses, particularly to those of the web-fed variety, and more particularly to a web-fed printing press of the kind having means for cutting off the web on the upstream side of a pair of printing cylinders in the event of accidental web break on the downstream side thereof during printing, in order to prevent too great a length of the web from sticking to, and wrapping around, either of the printing cylinders. Still more particularly, the invention pertains to improved means in such a printing press for more effectively dealing with web break.
In web-fed printing presses the paper is fed from a continuous paper roll or web roll and printed upon while passing between a pair of printing cylinders which may, for example, be blanket cylinders in the case of an offset perfecting press. The web travels past the blanket cylinders by being forcibly pulled in the downstream direction. Consequently, upon web break downstream of the cylinders, the upstream web will slacken and so readily stick to the cylinder or cylinders by reason of the adhesive force of the ink thereon. Eventually, were it not for means for web severance upstream of the cylinders, a substantial length of the web would wound around the cylinders with their continued inertial rotation.
A variety of solutions have been suggested and used in the printing industry in order to reduce the trouble ensuing from web break. One such solution, found in Japanese Unexamined Utility Model Publication No. 3-23439, teaches the use of an adhesive roller disposed downstream of the printing cylinders and movable into and out of rolling contact with a guide roller via the web, in combination with web cut means upstream of the cylinders and a web break sensor downstream thereof. The sensor senses a web break either from web slackening or from the nonrotation or reverse rotation of the guide roller, whereupon the machine suspends printing, and the web is cut off upstream of the printing cylinders. Further the adhesive roller is actuated into rolling contact with the guide roller via the severed, printed web, with the result that the web is coiled up on the adhesive roller as this roller rotates with the guide roller by inertia.
The adhesive roller that characterizes this prior art device has some shortcomings and inconveniences. First, in the case where an adhesive agent is previously applied to the roller, the adhesiveness of the roller was easy to deteriorate during the time web break did not occur, as a result of constant exposure to the air of the printing plant that is invariably laden with the paper fibers and particles from the webs. There were even cases where, when the web finally did break, the adhesive roller totally failed to perform the intended functions for lack or insufficiency of adhesiveness.
It is also contemplated in the same prior art device to apply an adhesive agent to the roller only upon web break, in response to the signal from the web break sensor. This practice is objectionable because of the unavoidable, unnecessary scattering-about of the adhesive agent, which stained the printing machinery and the floor and contaminated the air to the deterioration of the working environment.
An additional disadvantage manifested itself after the broken web had been successfully wrapped around the adhesive roller. Much labor and time had to be expended to remove the web from the roller and t o restore the roller to the workable state.
Japanese Unexamined Utility Model Publication No. 4-2635 and Japanese Patent No. 2523984 are alike in teaching web cut means disposed close both to the surf ace part of a printing cylinder just downstream of the printing position and to the web that has just been printed. Upon break downstream of the printing cylinders, the web will stick as aforesaid to the ink on either of the printing cylinders and so tend to wind round the cylinder in inertial rotation. The web cut means is intended to sever the web as it folds over itself in the course of its undesired winding round the cylinder. Japanese Patent No. 2523984, supra, additionally suggests the provision of a row of needles close to a cutting blade in order to perforate the web for positive severance.
The positioning of the web cut means close to the printing cylinders according to these known solutions is objectionable because, if one or both of these cylinders are blanket cylinders, for example, the web cut means hamper the mounting and dismounting of blankets to and from the cylinders, as well as the adjustment of the printing pressure and maintenance jobs in general. Moreover, inconspicuously mounted in confined regions between a printing cylinder and the web, the web cut means have represented a serious hazard to the workers from the viewpoint of labor safety. They have indeed been easy to have their fingers or hands injured by the cutter blades or perforating needles while working on the machine.
A further, and very serious, drawback is that, aside from the case where the row of perforating needles are provided, no means are provided for imparting tension to the web that has broken and that, consequently, has stuck to, and is going to wind around, the printing cylinder. The web has sometimes been left uncut for lack of tension even when it came into contact with the web cut means.